HZ value used in kernel/acct.c

[Tim Schmielau]

What is the supposed unit of the ac_etime field of struct acct?
The code in kernel/acct.c currently says

   ac.ac_etime = encode_comp_t(jiffies - current->start_time);

so it is given in multiples of HZ, which makes this value 
platform-dependent (and subject of overflow after 48.5 days with HZ=1024). 
In include/linux/acct.h however there is the definition

   #define AHZ             100

which somehow smells like the preferred time unit.
Comments?

Tim